I nt e r s ys t e mLocat i onUpdat e andPagi ngSchemesforMul t i
t i erWi rel essNet works * WenyeWangIanF.Akyildiz Br
oadband&Wi rel essNet wor ki ng Labor at or y Schoolof El ect
ri calandComput er Engi neer i ng Georgi a I nst i t ut e of
Technol ogy At l ant a, GA30332 {wenye,ian}@ece.gatech.edu ABSTRACT
Gl obalwi r el essne t wor ks e na bl emobi l e user st ocom-muni c
a t e r egar dl es s of t hei r l ocat i ons, Oneoft he mos t i
mpor t a nt i ssuesisl ocat i onma na ge me nt i na hi ghl ydyna mi
c e nvi r onme nt becaus emobi l euser s ma yr oa mbe t we e ndi f
f er ent wi r el essnet works~net -wor koper at or s~a ndgeogr aphi
cal r egi ons, I nt hi s paper~al ocat i ont r a c ki ngme c ha ni
s misi nt r oduced~ whi chconsi st sofi nt e r s ys t e ml ocat i
onupda t e s us i ng t heconcept of bounda r yl ocat i onar ea(
BLA) a nd pagi ngus i ngt heconcept of bounda r yl ocat i onreg- i
st er ( BLR) . The BLAisde t e r mi ne dbyadyna mi cl ocat i onupda
t e pol i cyi nwhi cht hevel oci t ya ndt he qual i t yof ser vi
ce(QoS)ar et a ke ni nt oaccount ona pe r - us e r basi s, The
BLRisus edt oma i nt a i nt he r ecor ds of mobi l euser scr ossi
ngt hebounda r yof net wor ks . Thi s me c ha ni s mnot onl yr
educes l oca- t i ont r a c ki ngcost sbut al sosi gni f i cant l
ydecr eases cal l lossr at es a ndaver agepagi ngdel ays. The per
-f or ma nc e e va l ua t i on oft hepr opos e ds chemes ispr o-vi
dedt ode mons t r a t e t hei r ef f ect i venessi nmul t i t i e
rwi r el essnet wor ks .1.I NTRODUCTI ON Fut
urewirelessnetworksaxeenvisioned asseamlessworld-
wideradiosystems,includingdiversenetworkbackbones
rangingfromhighcapacitypicocellnetworkstoterrestrial
microandmacronetworksaswellaslargesatellitesys-
tems[1,7,18].Theincreasing demandsforheterogeneous
servicesnecessitatehighqualitylocationmanagementt
hatallowsthewirelessnetworkstolocatemobile usersroaming *This
workis support ed by NSFunder grant NCR-97-04393 and by Korea
Telecom -Wireless Communications Research Laboratory(WCRL).
Permission to make digital or bard copies of all or part of this
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permissionand/or a fee. MOBICOM 2000BostonMAUSA Copyright ACM 2000
1-58113-197-6/00/08...$5.00 acrossdifferent networks.Location
managementis also crit- ical tomai nt ai n calls in progressas
mobile usersmove into a new service area.In general,location
managementcontains twoprocesses:location updat
eandpaging.Forstand-alone wireless networks, bot hof t hem have
been investigated com- prehensively over thepastdecade[2,5,6,21].In
thispaper wefocusonthelocationmanagement schemesforthemo-
bileterminals(MTs)roamingacrossmultitier wirelessnet-
workswithdifferenttechnologiesorprotocols.In[13], the
registration,calldelivery,andhandsetidentity forthehet- erogeneous
personal communication services(PCS)systems
werediscussed.Theregistration protocolsweremodified to
accommodatenetworksusing differenttechnologiessuchas
GSMandIS-41.In[23], theauthorssuggestedto"homoge- nize"the service
areasof two adjacent networks by filling the
biggersizecellswithsmallerones.Sothelocationupdat e andpaging would
beimplemented asinonenetwork. Also, it has been demonst rat ed in
[8] t hat the roaming across
networksimposesasignificantincreaseinsignalingtraf-
fic.Thetrafficanalysiswasbasedontheinterworkingof PCS1900and IS-41
systems by using a dual mode home loca- tion registration.In[17],
theinterworking between cordless and cellular
systems,e.g.,DECTandGSM,wasthoroughly
investigated.Thesignalingtrafficofintersystemlocation registration
and paging wasanalyzed based on different net-
workarchitectures.In[27], theintersystemlocationregis- t rat i
onwasstudiedonGSM/ PDCroamingandadditional interworking uni t s
wereproposedtocarryoutsignaling for- mat
transformationandauthentication. However,ineach of
theabovepapers,thesignaling costswerenotcomput ed basedonany
specific location updat eandpaging algorithm
andthequalityofservice(QoS)requirementssuchascall
lossandpagingdelaywerenotconsidered.
Inthispaper,anewlocationmanagement mechanismis introduced,
whichisapplicable totheintegration of hetero-
geneousnetworks.InSection2,thesystemmodelof multi-
tierwirelessnetworksisdescribed,basedontheconceptof
boundarylocationarea(BLA)andboundarylocationregis- ter(BLR).Then,
inSection3,theproceduresofintersys- tern location updat eand paging
axepresented,whichutilize theBLAsandBLRstosupportregistration
requestsand to locatemobile users.InSection 4,theprobabilities of
inter- 99 syst em roami ngarederived fordifferent mobi l i t y
models.In Section5,signalingcosts,calllossrates, andpagingdelays, i
nt roducedbyi nt ersyst emlocationupdat eandpaging,are demonst rat
ed. Finally, inSection6numericalresultsare provided, followedbyt
heconclusioninSection7. 2.SYSTEMDESCRI PTI ON Themul t i t i
erwirelessnetworkweconsideriscomprisedof
manynetworksusingdifferentst andardssuchasGSM, IS-
95,IS-54/136andsoon.Eachnetworkinagivengeograph- icalareawillt ypi
cal l ybesuppor t edbyaspecificnetwork operat or. Inthissectionwei
nt roduceasyst emarchi t ect ure t hat capt urest hehierarchicalst
ruct ureofmicrocellsand macrocells. 2.1Syst emArchi t ect ure
Inamul t i t i erwirelessserviceareaconsistingofdissimi-
larnetworks,itisdesirabletoconsidersomefactorswhich willinfluencet
heradi oconnectionsof t hemobilet ermi nal s (MTs)roami
ngbetweendifferentnetworks.Forexample,t hesignalingformat
sformicrocellandmacrocelltiersare different.Evenint hesametier, t
hesignalingformat, user i nformat i onandi dent i fi cat i on aut
hori zat i onaxe different for networksusingdifferentprotocols.As
showninFig.1,t here aretwonetworks, YandWint hemicrocell
tier,whichmay usedifferent prot ocol s suchas
DCS1800andPCS1900.Each hexagonrepresent sal ocat i onarea(LA)wi t
hi nast and- alonenet workandeachLAiscomposedofaclusterofmi-
crocells.Thet ermi nal sare requi red toupdat etheirlocation i
nformat i on wi t h t henetwork whenever t hey enter anew LA;
therefore,t henet workknowst heresidingLAofat ermi nalallt hetime.
Int hemacrocelltiert herearealsotwonet-
works,XandZinwhichdifferentprotocols(e.g.,GSMand IS-41)areapplied.
Formacrocellnetworks,oneLAcanbe onemacrocell.It ispossiblet hat
networksXandW, al- t houghindifferenttiers,mayempl
oysimilarprotocolssuch asIS-95,GSMoranyot herprotocol. Weconsidert
hetwo- t i ermodel t hroughout ouranalysis;however,t heproposed
scheme is appl i cabl e tot hemul t i t i er scenario by t aki ng
pairs of adj acent networks.-- IntrasystemRoamingI-- Intersystem
Roaming Figure1:Systemarchitectureofintrasystemand i
ntersystemroaming.Thereare twot ypes of roami
ngshowninFig.1:intrasystem orintersystemroaming. Int rasyst emroami
ngreferstoan MT' smovementbetweent heLAswi t hi nanetworksuchas
YandZ.Int ersyst era roami ngreferstot heMTst hat move
betweendifferentnetworks.Forexample, mobileusersmay
travelfromamacrocellnetworkwi t hi nanIS-41networkto aregiont hat
usesGSMst andard.2.2BoundaryLocationArea(BLA)and
BoundaryLocationRegister(BLR) Concepts Inourcontext, t hel ocat i
onmanagement inmul t i t i ernet- worktacklest hei nt ersyst
emroami ng, whichincludesin- t ersyst emlocationupdat
eandpaging.Thei nt ersyst emlo- cat i onupdat eisconcernedwi t
hupdat i ngt hel ocat i onin- format i onofanMTperformi ngi nt
ersyst emroami ng. The i nt ersyst em paging is concerned wi t
hsearching for t hecalled t ermi nal roami
ngbetweendifferentserviceareas.Thegoal of i nt ersyst
emlocationmanagement istoreducet hesignal- ingcostwhilemai nt ai ni
ngQoSrequirements. Forexampl e,reducingcall lossisoneof t
hekeyissuesinmai nt ai ni ngt he callconnection;decreasingt
hepagingdel ayiscriticalt o reducet hecallset -uptime.Fori nt
ersyst eml ocat i onupdat e, weconsideraboundar y
regioncalledboundarylocationarea (BLA)existingatt he boundar
ybetweentwonetworksindifferenttiers.Asillus- t r at
edinFig.2,networksXandYareint hemacrocell
andmicrocelltiers,respectively.Thereisahomel ocat i on
register(HLP~)foreachnetworkandauserisper manent l y associated
withanHLRinhi s/ hersubscri bednetwork. The
BLAiscontrolledbyaboundar yi nt erworki nguni t (BIU),
whichisconnect edtomobileswitchingcenters(MSCs)and visitor l ocat i
on registers(VLRs)in bot hnetworks. TheBIU is responsible forret ri
evi ngauser' sservicei nformat i onand t ransformi
ngmessageformats. Also,t heBIUisassumed tohandl esomeot
herissuessuchast hecompat i bi l i t y of air interfacesandt heaut
hent i cat i onof mobileusers.Thecon- figurationofaBIUdependsont
hetwoadj acent networks t hat thisBIUiscoordi nat i ng. Moredet ai
l scanbefound in[4,8,17,27]. (Macroccll~c~Tier)~ ~ 0
~(MicrocellTier) LA 3.~.' LA. . . . . . . .."" "MSC andVLR inX/MSC
and VLR inY BoundaryLocationArea(BLA) Figure2:Boundary
locationarea(BLA)and bound- arylocationregister(BLR).100
TheBLAisconsideredasadynami cregiondependi ngon eachMT' sprofile
suchas speed andbandwi dt hrequirement.WhenanMTent erst heBLA,
itsendsregi st rat i onrequest tot heBIUandt heBIUforwards this
requesttot henetwork t owardswhicht heMTismoving.Byusingt heBLAcon-
cept,anMTisallowedtoregisterandupdat eitslocation beforet
heMTreceivesormakescallsint henewnetwork. Inaddi t i ontot
heconceptof BLA, wedesignateaboundary
locationregister(BLR)tobeembeddedint heBIU.ABLR isadat
abasecachetomai nt ai nt heroami nginformation
ofMTsmovingbetweendifferentnetworks.Theroami ng i nformat i
oniscapt ur edwhent heMTrequestsalocation regi st rat i onint
heBLA. TheBLRsenablet hei nt ersyst em pagingtobei mpl ement edwi t
hi nt heappropri at enetwork t hat anMTis current l y residing in,t
hus reducing t he paging costs.Therefore,t heBLI% andt
heBIUareaccessibleto t hetwoadj acent networksandarecollocated
tohandl ethe i nt ersyst emroami ngof MTs.Ont hecontrary, t
heVLRand t heMSCprovide roami ng i nformat i onwithinanetworkand
dealwitht hei nt rasyst emroami ngofMTs.Besides,t here
isonlyoneBLRandoneBIUbetweenapai rof neighboring networks,but t
heremaybemanyVLRsandMSCswithin ast and-al onenetwork.3.I
NTERSYSTEMLOCATI ON UPD ATE AND PAG I NG SCHEMES
WhenanMTismovingacrossdifferentnetworks,itmustperformi nt ersyst
eml ocat i onupdat e, whichisbasedont he conceptofBLA. Tolocatet
heMTforcalldelivery,inter- syst empagingisrealizedt hroughBLR. 3 .
1I nt e r s ys t e mLocat i onUpda t e Usi ng BLAConc e ptWedefinet
heBLAofanMTtobet heregioninwhicht he MTsendsal ocat i on regi st
rat i on requesttot henewnetwork t owardswhicht hat
MTismoving.Anewlocationupdat e mechani smisusedsucht hat t heMTwill
report its location whenitsdi st ancefromt heboundar yis lesst
hanupdatedis- tance,d~v,det ermi nedby(1).Thislocationupdat escheme
guarant eest hat t heMTupdat esitslocationinformationin anareat hat
iswi t hi nadi st ancet hreshol dawayfromt he boundar
yoftwonetworks(tiers),XandY.Forexample,Fig.3showst hemovement pat
hofanMTmovingfrom networkXtoY.Assumet hi sMTperformeditslastloca-
tionupdat eint heLAwi t hi nXanditsupdat edistanceis d~. TheBLAof t
hi sMTist heregionwithind~fromt he boundar yinXandt
heregionwithind~inY. InorderforanMTtosendregi st rat i
onrequestfromXto Y,t heprocedure of i nt ersyst em location updat
eincludes t he followingsteps: 1.InnetworkX, t hebasest at i
ons(BSs)int heLAcon- tiguous toYbroadcast t hei r distances from t
hebound- aryof twonetworks(tiers)periodically.Thus,theMT candet
ermi ne its l ocat i on wi t h regard tot he boundar y byreceivingt
hei nformat i onfromt heBSs. 2.If t heMTfinds t hat it is wi t hi
nt heBLA by compari ng t hel ocat i oni nformat i onwithupdat et
hreshol dd~, it sendsani nt ersyst eml ocat i onupdat erequesttot
he BIUont heboundary. Ne t wor kX "~........." ~" ~' / "z"7~: ~Yt
~"-.~Mobi l e. ,' : dY x", , .[ , ~ .terminal( M T ) , , , I- . - ,
. . , . . - . . - . - - . . - . - - . - ( Mi e r oc e l l Ti e r
)Fi gur e 3:Locat i onupdat edi st anceandt heconceptof
BLA.3.TheBIUt ransformst hesignalingformat , aut hent i - catest
heuseridentity, sendsregi st rat i onrequeststo Y,andupdat est
heMT' sprofileint heBLR. Ift hi s MTneedscall connectionwhile roami
ng, its request is put int hecallconnectionqueueinY.
Theaboveprocessdependsont heBLAt hat , int urn, isde- pendent ont
heMT' supdat edistance. Adynami cl ocat i on updat epolicy is
developed todet ermi ne t heupdat edi st ance onaper-user
basis.Underthis scheme,t heupdat edistance,d~for t heMTmoving from
Xto Yis based on t hefollowing considerations: Velocity~.
IfanMTismovingveryfast,itmayar- riveatt henewnetworkinashort time.
Thus, t he updat edi st anceshouldbelongsot hat t heMTcan sendt hel
ocat i onupdat emessageandfinishlocation regi st rat i
onbeforeitenterst henewnet workY.The
velocityratiov~isdefinedasv~=G/v=,wherev~is t
heaveragespeedofallMTsinmacrocellnetworkX.QoSfactor71.~1 ist herat
i ooft hebandwi dt hre- quiredbyanMTtot hebandwi dt havailableint
he newnetworkwhent hemul t i medi a serviceis
provided.Ifr/0)ofaMarkovchainast he di st ancebet weent hecurrent
locationoft heMTandt he centeroft heLA. Thi sst at eisequivalenttot
heindexof aringinwhicht heMTislocated. Asaresult,t heMTis
saidtobeinst at ekifitiscurrent l yresidinginringrk. Thet ransi t i
onprobabi l i t i es ak, k+land/3k,k-1representt he probabi l i t i
es at which t hedi st ance of t heMTfrom t he center cellof
anLAincreasesanddecreases,whicharegivenas: ( l - q) if k= 0,ak, k+l
=( 1- - q)(+~) i f l < k< K, (6) /~k,k-1=(1-q)(-~-~)if1